This application is based on Application No. 2001-172704, filed in Japan on Jun. 7, 2001, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a control unit for an internal combustion engine, and more particularly to a power supply system for an internal combustion engine control unit.
2. Description of the Related Art
FIG. 4 illustrates the configuration of such a kind of known power supply system for a control unit of an internal combustion engine, in particular for marine use. In this figure, a hull 1 of a marine vessel or boat includes a stop switch 4 which is depressed into a connected (on) state to generate a signal representative of that state when the driver indicates his or her intent of stopping driving, a main switch which is depressed into a connected (on) state to generate a signal representative of that state when the driver indicates his or her intent of driving, a battery 6 for supplying electric power to respective devices of the marine vessel including an outboard unit 2, and a connector 7 for connecting a power supply line from the battery 6 to the outboard unit 2 as well as various signal lines from the stop switch 4, the main switch 5 and other devices (not shown) to the outboard unit 2.
In this connection, note that the stop switch 4 is normally in an open (off) state, whereas the main switch 5 is normally in a connected (on) state, as illustrated in FIG. 5.
The outboard unit 2 includes an internal combustion engine control unit (ECU) 3 with a built-in CPU (not shown) for detecting the above signal states and controlling the related devices (not shown in particular) installed on the outboard unit 2 thereby to perform various control operations such as ignition timing control, injection amount control, etc.
In the marine vessel, an operation panel, which is operated by the driver, is arranged at the front portion of the hull 1, and it is necessary to arrange signal-related component parts such as the main switch 5 acting as a power switch, the stop switch 4, a throttle (not shown), etc., on the operation panel. Accordingly, these signal-related component parts are connected with the ECU 3 installed on the outboard unit 2 through one or more harnesses 12 of a several meter length.
That is, the signals from the main switch 5 and the stop switch 4 as well as the power supply from the battery 6 are input to the ECU 3 through the connector 7 and the harness 12 so that various control operations are carried out by the ECU 3.
With the known power supply system for a control unit of an internal combustion engine as constructed above, the outboard unit 2 in the form of a marine internal combustion engine (hereinafter simply referred to as engine) is used on the surface of water such as a sea, a lake or the like, and hence corrosion is liable to take place on the various kinds of harnesses. Particularly, the connecting portions of the harnesses at which connectors are used for frequent connections and disconnections are easily subjected to corrosion.
When corrosion has occurred, reliability in the signal transmission at the connecting portions reduces, giving rise to a situation in which the signal transmission may be abnormal. If such corrosion is generated in the power supply line supplying power to the ECU and the like, which controls the engine, there will be a possibility that the engine can not be started or stops suddenly.
With a recent engine equipped with a fuel injection system, the engine can not be operated if not properly supplied with power. On the other hand, with an old or former engine employing a carburetor and a CDI ignition device, the entire system is constructed such that the engine can be operated without any battery power supply, and hence the influence of corrosion is limited. However, since a recent emission control compliant model adopts fuel injection, the power supply from a battery is required. Therefore, the degree of influence of the above-mentioned corrosion is increasing.
As described above, the power supply harness for supplying electric power from the power supply in the hull to the ECU, etc., in the outboard unit becomes long due to the construction that the hull and the outboard unit are arranged apart from each other. In addition, it is necessary to arrange the signal harness for signal transmission between the ECU of the outboard unit and the main switch, the stop switch, the throttle, etc., in the operation panel at the front portion of the hull in such a manner that the signal harness extending from the inboard elements in the operation panel is connected through the connector with the ECU, etc., in the outboard unit.
Thus, there is a problem that reduction in the reliability of the harnesses may frequently take place at the connectors, and hence in the worst case, the power supply to the ECU, etc., in the outboard unit may be stopped due to contact failure such as an instantaneous power interruption, etc.
Moreover, an additional problem is that if the engine is stopped suddenly and can not be restarted due to contact failure at the connectors or the like of the harnesses after a marine vessel or boat installing the engine has departed from a port, the marine vessel will not be able to return to the port, thus leading to a distress and a serious influence on the lives of passengers.
The present invention is intended to obviate the problems as referred to above and has for its object to provide a power supply system for a control unit of an internal combustion engine which has the function of maintaining the power supply to an internal combustion engine control unit and its related devices after an internal combustion engine has once been started until an ECU detects a driver""s intent of stopping the engine, thereby holding the engine in an operable condition thereof.
Bearing the above object in mind, the present invention rsides in a power supply system for a control unit of an internal combustion engine, comprising: a power supply line exclusively used for supplying electric power from a battery to an internal combustion engine control unit and its related devices; a relay having a self holding function and inserted in the power supply line for switching between supplying and interruption of electric power; and the internal combustion engine control unit adapted to receive electric power from the battery through the power supply line. The internal combustion engine control unit comprises: an arithmetic processing section which performs arithmetic processing for various control operations of the internal combustion engine control unit, receives a main switch signal representative of an on/off state of a main switch, which is in an on state during operation of the internal combustion engine, and a stop switch signal representative of an on/off state of a stop switch, which is made into an on state when the internal combustion engine is stopped, outputs and holds a relay drive signal when the main switch signal indicates the on state of the main switch, and stops outputting the relay drive signal when the stop switch signal indicates the on state of the stop switch; and a relay drive and hold circuit which receives the relay drive signal and the main switch signal, drives the relay into a power supplying state and holds this state as long as at least one of the main switch signal indicating the on state of the main switch and the relay drive signal from the arithmetic processing section is input to the relay drive and hold circuit.
In a preferred form of the present invention, the battery is arranged at a location apart from the internal combustion engine control unit and the relay, and the power supply line is directly connected from the battery to an internal combustion engine control unit side.
In another preferred form of the present invention, the power supply system is used for a marine internal combustion engine control unit of a marine vessel. The battery is arranged in a hull of the marine vessel, and the internal combustion engine control unit and the relay are arranged in the outboard unit. The power supply line comprises a harness which is directly connected from a hull side to an outboard unit side.
In the present invention, a power supply system is constructed such that it includes a stop switch indicating a driver""s intent of stopping driving for example and usually generating an open signal representative of an open (off) state thereof, a main switch indicating a driver""s intent of driving for example and usually generating a connection signal representative of a connected (on) state thereof, a relay for supplying electric power from a battery to an internal combustion engine control unit and various kinds of related sensors and actuators, and an ECU having a CPU incorporated therein for detecting engine operating conditions such as the number of revolutions per minute of the engine, the engine temperature, etc., based on signals from the various kinds of sensors. Here, the relay for supplying electric power to the internal combustion engine control unit and its related respective devices is constructed such that it is driven to operate under the control of the ECU, whereby the engine is held in an operable state until the driver has the intent of stopping the engine.
With such a construction, even when corrosion occurs in various kinds of signal harnesses or the like, causing contact failure, breaks, etc., it is possible to ensure the supply of electric power to the internal combustion engine control unit and its related various devices, thus permitting the engine to be driven to operate even in such a situation. As a result, it is possible to prevent the engine from being stopped against a driver""s will and becoming unable to restart.